Nicotine biological activity

Niacin (Fig. 1) is a collective name for all vitamers having the biological activity associated with nicotinamide (= pyridine-3-carboxamide), including nicotinic acid (= pyridine-3-carboxylic acid) and a variety of pyridine nucleotide structures. 

Nicotinamide and nicotinic acid are both white crystalline substances. Their aqueous solution has a maximal UV absorbance at 263 nm. Both vitamers have the same biological activity as they can be converted into each other. Figure 2 shows the structure of the coenzyme forms NAD+ and NADP+. 

Niacin was discovered as a nutrient during studies of pellagra. It is not strictly a vitamin since it can be synthesized in the body from the essential amino acid tryptophan. Two compounds, nicotinic acid and nicotinamide, have the biologic activity of niacin its metabolic function is as the nicotinamide ring of the coenzymes NAD and NADP in oxidation-reduction reactions (Figure 45-11). About 60 mg of tryptophan is equivalent to 1 mg of dietary niacin. The niacin content of foods is expressed as mg niacin equivalents = mg preformed niacin + 1/60 X mg tryptophan. Because most of the niacin in cereals is biologically unavailable, this is discounted. 

These include nicotinic acetylcholine receptors, neuronal calcium channels, muscle sodium channels, vasopressin receptors, and iV-methyl-D-aspartate (NMDA) receptors. Some general features of the structure, function, and evolution of biologically active peptides isolated from Conus venom are presented. 

Niacin is a generic name for a small family of molecules having niacin biological activity. The most common structures that fall into this category are nicotinic acid and nicotinamide ... 

True alkaloids derive from amino acid and they share a heterocyclic ring with nitrogen. These alkaloids are highly reactive substances with biological activity even in low doses. All true alkaloids have a bitter taste and appear as a white solid, with the exception of nicotine which has a brown liquid. True alkaloids form water-soluble salts. Moreover, most of them are well-defined crystalline substances which unite with acids to form salts. True alkaloids may occur in plants (1) in the free state, (2) as salts and (3) as N-oxides. These alkaloids occur in a limited number of species and families, and are those compounds in which decarboxylated amino acids are condensed with a non-nitrogenous structural moiety. The primary precursors of true alkaloids are such amino acids as L-ornithine, L-lysine, L-phenylalanine/L-tyrosine, L-tryptophan and L-histidine . Examples of true alkaloids include such biologically active alkaloids as cocaine, quinine, dopamine, morphine and usambarensine (Figure 4). A fuller list of examples appears in Table 1. 

Niacin is also known as vitamin PP or vitamin Bj. The term niacin describes two related compounds, nicotinic acid and nicotinamide (Figure 19.18), both with biological activity. Niacin is formed from the metabolism of tryptophan, and therefore it is not strictly a vitamin. It is a precursor of two cofactors nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which are essential for the functioning of a wide range of enzymes involved in redox reactions. 

In the form in which they are consumed, many vitamins are not biologically active. For several water-soluble vitamins such as thiamine, riboflavin, nicotinic acid, pyridoxine, activation includes phosphorylation or, as is the case with riboflavin and nicotinic acid, coupling to purine or pyridine nucleotides is required. In their major known actions, water-soluble vitamins participate as cofactors for specific enzymes, whereas at least two fat-soluble... 

In general, plants do very well in their environments, notwithstanding the omnipresence of a multitude of potential insect herbivores and a number of vertebrate herbivores as well. Some plant species are very insecticidal, as a consequence of their producing a variety of alkaloids including nicotine, piperine, lupine alkaloids, steroidal alkaloids, ephedrine, berberine, strychnine, gramine, and caffeine.37 These biologically active alkaloids also function as deterrents. In terms of families, caffeine is the the most widely distributed alkaloid, a fact that may be... 

In humans and animals, chromium(ni) is an essential nutrient that plays a role in glucose, fat, and protein metabolism by potentiating the action of insulin (Anderson 1981). The biologically active form of chromium, called glucose tolerance factor (GTF), is a complex of chromium, nicotinic acid, and possibly amino acids (glycine, cysteine, and glutamic acid). Both humans and animals are capable of converting... 

There have been no studies on the biological activity of the above quinolizidine alkaloids. It is expected that they, like the 5,8-disubstituted indolizidines and other lipophilic dendrobatid alkaloids, will be noncompetitive blockers of nicotinic receptor-channels. 

The biological activity of noranabasamine has not been assessed. Anabaseine and other bipyridyl alkaloids are toxic and have nicotine-like effects (166,167). 

Nicotinic acid and nicotinamide have equal biological activity. As discussed in Section 8.3, approximately 60 mg of tryptophan is equivalent to 1 mg of... 

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